Digitizer cursor coil for reducing edge effect

Abstract

A digitizer cursor coil for use as part of a digitizer is disclosed. The cursor coil includes a primary winding and a secondary winding concentric with the primary winding and having a larger diameter than same. The windings are connected together in series such than when they are energized, current flow in the primary coil is in a direction opposite to the direction of the current flow in the secondary coil. The digitizer cursor includes a lens assembly comprising a bottom core and a top core both of which are formed from a disk shaped transparent material. The primary winding is wrapped into a groove formed in the bottom core, the secondary winding is wrapped into a groove formed in the top core. Cross hairs and a cross hair center point are formed in the bottom core. The top core is movable relative to the top core so that when the cursor coil is energized the center point of the magnetic field formed thereby can be aligned with the cross hair center point.

I claim: 
     
       1. A digitizer cursor coil for use in a digitizer cursor used as part of a digitizer assembly, comprising: (A) a primary winding formed of conductor wrapped into a first coil of a selected diameter; and   (B) a secondary winding formed of a conductor wrapped into a second coil, said second coil being substantially concentric with said first coil and having a diameter greater than said first coil, said conductors forming said primary and secondary windings being connected together in series such that when said conductors are energized, current flow in said primary winding is a first direction and in said secondary winding in a second direction opposite said first direction.   
     
     
       2. The digitizing cursor coil of claim 1 wherein at least one of said windings can be adjustably positioned relative to the other of said windings. 
     
     
       3. The digitizer cursor coil of claim 1 wherein said cursor coil is assembled with a lens assembly that is part of the digitizer assembly, said lens assembly formed of transparent material having at least one reference marking thereon, said reference marking defining at least one reference point. 
     
     
       4. The digitizer cursor coil of claim 1 wherein said cursor coil is assembled with a lens assembly that is part of the digitizer assembly, said lens assembly formed of transparent material have a set of cross hairs thereon, said cross hairs arranged to define a cross hair center point. 
     
     
       5. The digitizer cursor coil of claim 4 wherein at least one of said windings forming the digitizer cursor coil can be selectively positioned relative to said lens assembly so that when said digitizer cursor coil is energized, the cursor coil generates a magnetic field having a center point aligned with said cross hair center point. 
     
     
       6. A digitizer cursor for use as part of a digitizing device, comprising: A. a bottom core composed of transparent material formed in the shape of a disk, having a selected first diameter, said bottom core having an annular outer surface therearound,   B. a top core composed of transparent material formed in the shape of disk having a second diameter greater than the bottom core first diameter; and   C. a cursor coil including: (i) a primary winding formed of a conductor wrapped around said bottom core outer surface,   (ii) a secondary winding formed of a conductor wrapped around said top core outer surface; and   (iii) said conductors forming said primary and secondary windings connected together in series so that when said conductors are energized, current flows in said primary winding in a first direction, and in said secondary winding in a second direction opposite said first direction.     
     
     
       7. The digitizer cursor of claim 6 wherein A. a bottom groove is formed in the bottom core around the outer surface thereof;   B. a top groove is formed in the top core around the outer surface thereof;   C. the conductor forming said primary winding is wrapped in said bottom core annular groove; and   D. the conductor forming said secondary winding is wrapped in said top core annular groove.   
     
     
       8. The digitizer cursor coil of claim 6 wherein at least one of said cores can be selectively positioned relative to the other of said cores. 
     
     
       9. The digitizer cursor coil of claim 6 wherein at least one of said cores has formed therewith at least one reference marking thereon, said reference marking defining at least one reference point. 
     
     
       10. The digitizer cursor coil of claim 6 wherein at least one of said cores has a set of cross hairs formed therewith, said cross hairs arranged to form a cross hair center point. 
     
     
       11. The digitizer cursor coil of claim 10 further including at least one of said cores being selectively positioned so that when said conductors forming said primary and secondary windings are energized, the cursor coil generates a magnetic field formed having a center point aligned with said cross hair center point. 
     
     
       12. The digitizer cursor of claim 6 further including: A. said top core including a downward extending annular tab having a selected thickness; and   B. said bottom core including an upward extending annular flange having a top surface, said flange forming an annular groove having a selected width in the top surface thereof, said groove having a diameter substantially equal to the diameter of said top core annular tab; the width of said groove being wider than the thickness of said top core tab, so that when said top core is positioned over said bottom core such that said top core tab is positioned in said bottom core flange groove, said top core is allowed a limited degree of movement relative to said bottom core.   
     
     
       13. The digitizer cursor of claim 12 further including: A. a bottom groove is formed in a bottom core around the outer surface thereof;   B. a top groove is formed in the top core around the outer surface thereof;   C. the conductor forming said primary winding is wrapped in said bottom core annular groove; and   D. the conductor forming said secondary winding is wrapped in said top core annular groove.   
     
     
       14. The digitizer cursor coil of claim 12 wherein at least one of said cores has formed therewith at least one reference marking thereon, said reference marking defining at least one reference point. 
     
     
       15. The digitizer cursor coil of claim 12 wherein at least one of said cores has a set of cross hairs formed therewith, said cross hairs arranged to form a cross hair center point. 
     
     
       16. A digitizer cursor coil for use in a digitizer cursor used as part of a digitizer assembly, comprising: (A) a primary winding formed of conductor wrapped into a first coil of a selected diameter; and   (B) a secondary winding formed of a conductor wrapped into a second coil, said second coil being substantially concentric with said first coil and having a diameter different than said selected diameter of said first coil, said conductors forming said primary and secondary windings being connected together in series such that when said conductors are energized, current flow in said primary winding is a first direction and in said secondary winding in a second direction opposite said first direction.   
     
     
       17. The digitizing cursor coil of claim 16 wherein at least one of said windings can be adjustably positioned relative to the other of said windings. 
     
     
       18. The digitizer cursor coil of claim 16 wherein said cursor coil is assembled with a lens assembly that is part of the digitizer assembly, said lens assembly formed of transparent material having at least one reference marking thereon, said reference marking defining at least one reference point. 
     
     
       19. The digitizer cursor coil of claim 16 wherein said cursor coil is assembled with a lens assembly that is part of the digitizer assembly, said lens assembly formed of transparent material have a set of cross hairs thereon, said cross hairs arranged to define a cross hair center point. 
     
     
       20. The digitizer cursor coil of claim 19 wherein at least one of said windings forming the digitizer cursor coil can be selectively positioned relative to said lens assembly so that when said digitizer cursor coil is energized, the cursor coil generates a magnetic field having a center point aligned with said cross hair center point.